How to bake a fake SSS map (thickness map)
Note: you must use a version above 2.79 to have access to the AO node: https://builder.blender.org/download/


Create an Emissive shader then add an Input > Ambient Occlusion. Check Inside and Only Local (surrounding objects won't affect the AO). For the distance I have used 0.4 on Suzanne but you can tweak it depending on the model and scale (don't forget to apply the scale with Ctrl + A > scale).



To add blood directly on your model:


add a Mix node and set the first color to black, connect the inverted AO to the second slot. The factor of the node allow you to adjust the amount of blood that will be visible.
Add another mix node, connect the previous mix node to the factor, do not display too much blood. Set the first color to the base color and the second to the blood color. For the blood you can use R: 0.7 GB: 0.1.
Optionally overlay it to an Input > Geometry Pointiness node, use a Converter > ColorRamp at 0.45-0.55 to contrast it.
Finally multiply it to an Ambient Occlusion map if you use an emissive shader, otherwise the AO will be added with your scene's lighting.





Tip: you can adjust the samples of the AO depending on how much visible it is to render or bake faster.